The present invention relates to an apparatus for providing power steering assistance for steering a vehicle.
Many vehicles, such as trucks, are difficult or impossible to steer without some sort of power steering assistance. Often, power steering assistance is provided for a vehicle by pressurized hydraulic fluid from an engine driven pump. However, the engine driven pump does not provide pressurized hydraulic fluid when the engine is somehow disabled, or the pump malfunctions.
As a safety feature, it has been suggested that a second pump for supplying pressurized hydraulic fluid be used to provide auxiliary or backup power assistance. In one system, the second pump is driven by rotation of a ground engaging wheel. Operation of the second pump by the ground-engaging wheel ensures that pressurized hydraulic fluid is provided for power steering when the vehicle is moving, irrespective of the condition of the engine and/or the engine driven pump.
It is recognized that pressurized hydraulic fluid from the second pump should be supplied for steering assistance immediately following engine or engine driven pump disablement. It is also recognized that a means for controlling the selection of one of the two pumps for supplying the pressurized hydraulic fluid should be directly related to the operating condition of the engine or engine driven pump. It is further recognized that the means for controlling should not be unduly complicated to minimize the possibility of a malfunction. Moreover, it is recognized that the means for controlling should not be restrictive to the flow of pressurized hydraulic fluid from the engine driven pump when the engine driven pump is functioning.